High grade gliomas, especially glioblastoma (GBM), have exceptionally poor prognosis and cancers that metastasize to the brain, for example from the lung and breast are associated with advanced disease. Notably, our Multi-PI research team has discovered that casein kinase-1 delta and epsilon (CK1?, CK1?) are new therapeutic targets for GBM. This discovery originated from a small molecule screen by the Roush lab at Scripps Florida, who identified a class of highly potent and selective dual inhibitors of CK1? and CK1?. Further studies by the Duckett lab then showed that; (i) 11% of GBMs and 36% of all breast cancers have amplified CSNK1D; (ii) GBM and certain breast cancers including those that metastasize to the brain express elevated levels of CK1? and Wnt/?-catenin transcription targets; (iii) brain metastatic lung adenocarcinoma cells that express CK1? and CK1? and are highly sensitive to our inhibitors; (iv) dual CK1?/? inhibitors induce rapid apoptosis of GBM, breast and lung cancer cells ex vivo, and tumor regression in vivo, but are not toxic to normal human epithelial cells and can be administered daily to mice long term without observable adverse side effects; (v) CK1?/? regulates expression of key factors involved in tumor cell invasion, (vi) CK1?/? regulates expression of essential DNA damage repair genes, and (vii) inhibition of CK1?/? augments the killing effects of IR, DNA damaging chemotherapeutic agents and PARP inhibitors. Collectively these findings support the premise that CK1? is an exploitable target of GBM and other refractory cancers that metastasize to the brain. In Aim 1, using already established critical path assays, a validated research operating plan (ROP), an iterative medicinal chemistry approach based on a multi-parameter optimization strategy augmented by drug metabolism and pharmacokinetic studies, we will develop and deliver optimized dual and isoform selective brain penetrant CK1? and CK1? inhibitors. Efficacy and safety of these inhibitors will be tested in our intracranial human xenograft models in mice. In Aim 2, we will (i) identify the full cast of invasion related protein(s) modified by CK1? activity, (ii) elucidate how CK1? contributes to GBM tumor cell diffusion; (iii) determine how and at which stage CK1? control aspects of the metastasis cascade from the periphery to the brain, and (iv) elucidate the role of CK1? in regulating a glioma stem cell-like state. In Aim 3, we will determine; (i) the MOA of DNA damage- induced CK1?-regulation of genome maintenance pathways in GBM, and (ii) define the safety margin associated with our lead CK1?/? inhibitor and the most efficacious combination for improved treatment in GBM.